Effects of some selective serotonergic (5-HT) antagonists on methamphetamine-induced anorexia were investigated in male mice. The least possible dose of methamphetamine alone that caused significant anorectic activity was 11 mumol kg(-1), i.p. (2 mg kg(-1)). Various doses of some selective serotonergic receptor antagonists were administered half an hour before the above mentioned dose of methamphetamine. Methiothepin potentiated, whereas NAN-190, methysergide, mianserin and ondansetron antagonized methamphetamine-induced anorectic activity. The least possible doses of these antagonists which modified methamphetamine-induced anorexia were as follows: methiothepin (1.1 mumol kg(-1), i.p.), NAN-190 (4.2 mumol kg(-1), i.p.), methysergide (2.1 mumol kg(-1), i.p.), mianserin (3.3 mumol kg(-1), i.p.) and ondansetron (0.003 mumol kg(-1), i.p.). The serotonergic antagonists at the above mentioned doses did not modify the food intake of animals not treated with methamphetamine, except for methiothepin, which produced a significant reduction, and mianserin, which produced a significant increase in food intake. The results of the present study indicated that the anorectic activity induced by methamphetamine is related to the interactions of methamphetamine with 5-HT receptor. Since a very small dose (0.003 mumol kg(-1)) of ondansetron (the 5-HT3 antagonist), as compared with the other antagonists used in this study, antagonized the anorexia induced by methamphetamine, the 5-HT3 receptor is likely to be the site for this interaction. (C) 2004 Published by Elsevier Ltd.